Field of the Invention
The present invention relates to a radiometric density profile measuring arrangement as well as a method for the radiometric detection of a density profile.
Background of the Invention
Various radiometric measuring arrangements are known from prior art for determining density profiles. These measuring arrangements are used in order to detect in a touchless fashion the distribution of layers of various bulk materials, for example in a container or a tank, characterized in their density.
An exemplary application for this method is the detection of different layers used in oil production. In oil production, for example sand, water, and crude oil are produced and collected in a tank, with the sand sedimenting, and crude oil and water separating in layers. For the further processing it is necessary to isolate the layers from each other and to separate sand and water from the crude oil, which can occur for example by draining some content of the tank in a lower section of said tank. In this method it is crucial to drain only water and sand, to the extent possible, and this way prevent wasting any crude oil.
Due to the fact that the materials given here differ in their density, appropriate density measuring arrangements and methods are applied.
The radiometric density measurement is here particularly characterized in that a measurement is possible independent from process conditions inside the tank and independent from the concrete chemical composition of the bulk materials to be measured. In particular, any potentially corrosive features are irrelevant, because the necessary measuring devices can be arranged outside the tank.
The underlying measuring principle utilizes the density-dependent absorption of gamma quanta in various media. For this purpose, gamma quanta are emitted from one or more radiation sources by the measuring device in the direction towards the bulk materials to be measured in order to detect the radiation intensity arriving there. Depending on the density of the bulk material located between the radiation source and the measuring device, more or less gamma quanta are absorbed by the bulk material, so that the radiation intensity at the location of the measuring device represents an indicator for the density of the bulk material.
Here, a detection of the radiation intensity usually occurs with the help of a so-called scintillation counter, which essentially comprises a scintillator for converting the gamma radiation into light pulses and a downstream arranged photomultiplier for generating electric impulses from said light pulses. The electric impulses are further processed, for example amplified and counted in measuring electronics arranged downstream. The number of the detected pulses is representative for the radiation intensity and thus also for the density of the bulk material. The fewer pulses are detected the higher the density of the bulk material.
In the methods of prior art, in a lower section of the tank the density is monitored in the area of a minimum fill level, which may not be fallen short of by the separating layer between water and crude oil, using a single measuring device. In the event that for example additionally a maximum fill level shall be monitored, for example for the water or the sand, here accordingly additional measuring devices are necessary, which are arranged at the respective fill levels.
In order to detect the composition of a multi-layered arrangement comprising bulk materials or to detect a density profile, many more measuring devices must be provided.
A respective arrangement is illustrated in FIG. 5.
FIG. 5 shows a radiometric density profile measuring arrangement 1 according to prior art, in which inside a tank 100 a multitude, in the present case six, radioactive radiation sources 3 are arrangement. The radiation sources 3 are arranged in a lance 4 and aligned such that their radiation cones 31 define a vertical radiation level, in which a number of detection units and/or measuring devices 5 is arranged, corresponding to the number of radiation sources 3. As discernible from FIG. 5, corresponding to the six radiation sources 3 provided, horizontally offset six vertically distributed measuring devices 5 are arranged according to the radiation sources 3.
By a horizontal arrangement of a measuring device 5 in reference to a radiation source 3 a density measurement can occur respectively at a fill level h and this way a density profile of the bulk material 99 located in the tank can be detected.
In another method known from prior art, respectively one radiation source and one measuring device allocated to said radiation source is moved vertically along or within the bulk material, and this way a density profile is detected.
The objective of the present invention is to simplify the detection of the density profile.
This objective is attained in a radiometric density profile measuring arrangement with the features of claim 1 and a measuring method for the radiometric detection of a density profile according to claim 13. Advantageous further developments are the objective of the dependent claims.